(a) Field of the Invention
The present invention relates to a thermosensitive recording material suitable for use in information devices such as facsimiles, printers, data communication parts and computer terminals.
More specifically, the present invention relates to a thermosensitive recording material having excellent color development sensitivity which meets the high speed requirements of information devices such as facsimiles.
(b) Description of the Related Art
A thermosensitive recording material can be obtained, for example, by dispersing a colorless or light-color leuco dye as a color former and a phenolic compound such as bisphenol A as a developer in a binder, then coating a substrate such as a paper with the resulting dispersion and drying the same.
The thus obtained thermosensitive recording material develops a color with the aid of heat from a heating head or exothermic pen, whereby an image record can be easily obtained. For this reason, the thermosensitive recording material is used in many fields such as information devices such as facsimiles, thermal printers, data communication parts and computer terminals as well as labels, tickets and passes.
Particularly, the temperature of the thermal head on the exothermic pen of such devices becomes lowered along with the increased speed and miniaturization of such information devices. Accordingly, it is desired that the thermosensitive recording material to be used therein has a high color development sensitivity.
One process for increasing the speed of the color development is to raise the temperature of the thermal head. However, when the temperature of the thermal head is elevated, problems such as the adhesion of dregs and sticking tend to occur and the life of the thermal head is also shortened. Thus, the above-mentioned process is not practical.
Japanese Laid-open Patent Publication No. 59-143683 discloses a technique in which crosslinked styrene microparticles are present in a color development layer in order to prevent the adhesion of dregs, sticking and pressure color development by scratching. However, this technique is not practical because sharp images having a high density cannot be obtained thereby.
Another technique has also been suggested in which a heat insulating intermediate layer containing thermoplastic hollow fine grains is interposed between a substrate and a thermosensitive color development layer so as to effectively apply the heat of the thermal head to the thermosensitive color development layer, whereby sharp images having a high density can be obtained (Japanese Patent Laid-open Publication Nos. 62-117787 and 63-21180). In this process, however, the fine grains themselves are melted by the heat, so that the adhesion of dregs on the thermal head and sticking take place noticeably, which means that the above-mentioned technique is not practical.